In an optical communication network represented by Fiber To The Home (FTTH), a bi-directional communication system has become widely used. The bi-directional communication system connects a communication office with a user through a single optical fiber and bi-directionally communicates using two kinds of light with different wavelengths as a transmission signal and a reception signal, respectively.
There is such a module as disclosed in Patent Document 1 (Japanese Patent Publication H10-206678) as an example of a bi-directional communication module used in this system. In the module according to Patent Document 1, a laser module as a transmission part and a photodiode as a reception part are packaged separately. Such modules (transmission module and reception module) are as a whole packaged together with a wavelength branching filter (wavelength filter) to branch out light for transmission and light for reception. This realizes two-way communication.
However, in the system according to Patent Document 1, a transmission module and a reception module packaged have to be adjusted separately (in adjustment of an optical axis and the like), resulting in a higher manufacture cost. There is also a problem, in which a whole module becomes larger in size to make miniaturization difficult.
A bi-directional communication module according to Patent Document 2 (Japanese Patent Publication 2006-154535) and the like has been proposed as a way to solve such problems. The module according to Patent Document 2 and the like mounts a transmission part, a reception part and a wavelength filter together on a single substrate. This realizes miniaturization and lower-costing of the optical communication module.
FIG. 1 is a perspective view illustrating a structure of a conventional bi-directional communication module disclosed in Patent Document 2. FIG. 2 is a side view illustrating an appearance of FIG. 1 observed from Side A (receiving end) and Side B (transmitting end). In FIGS. 1 and 2, an alignment mark 109 used to align with the element when mounted and V-grooves 101, 102 with a V-shape cross-section when laterally observed are formed by anisotropic etching on a silicone substrate 100 as a support substrate. A laser chip (LD) 103 of emitting light for transmission, a lens at the transmitting end 104, a lens at the receiving end 105, a light receiving element (PD) of converting an optical signal to an electric signal 106, a glass element 107 and a wavelength filter 108 are mounted on this substrate 100 to manufacture the optical communication module.
A method of bi-directional communication by an optical communication module disclosed in Patent Document 2 is next described. FIG. 3 is a plan view illustrating an optical path in a conventional optical module shown in FIG. 1. FIG. 4 is a side view illustrating the optical path divided into the receiving end and the transmitting end in the conventional optical module shown in FIG. 1. As shown in FIGS. 3 and 4, light for transmission 119 emitted from LD 103 is collimated by a proximal lens 104 when transmitted, followed by passing through a wavelength filter 108 to converge by a ball lens 114 to an optical fiber 112.
Light for reception 120 emitted from the optical fiber 112 is diffracted by a ball lens 114 when received, followed by refracting by 90 degrees at a reflection film of a wavelength filter 108 to reach a lens at the receiving end 105. After light for reception 120 is diffracted at a lens 105, it passes through a V-groove 102 at a side of light for reception to be reflected at a reflection plane (not shown) formed on an end plane of a V-groove 102, reaching a plane of light for reception of PD106 mounted on the top surface therein through a glass element 107.
In the bi-directional communication according to the above system, each of LD 103 and PD 106 mounted on one substrate has to be electrically and optically separated (insulated) in order to prevent an effect of noises. A glass element 107 is thus configured between a substrate 100 and PD 106 and an adhesive 122 is used to adhere the substrate 100 to the glass element 107.
FIGS. 5-7 are top and side views illustrating part of processes of assembling a conventional optical communication module shown in FIG. 1. A state prior to application of an adhesive resin, a state posterior to application of the adhesive resin and a state after mounting the element on the adhesive resin are illustrated in FIG. 5, FIG. 6 and FIG. 7, respectively.
After starting the state shown in FIG. 5, the adhesive resin 122 is applied around V-grooves 101, 102 on the substrate 100 as shown in FIG. 6. As shown in FIG. 7, the adhesive resin is then thermally cured to adhere while pressing the glass electrode 107.
FIG. 8 is an illustrative view (side view) showing problems with a conventional optical communication module shown in FIG. 1. FIG. 9 is an illustrative view (side view of an optical path at the receiving end) showing problems with the conventional optical communication module shown in FIG. 1.
As shown in FIG. 8, such a conventional system as above causes problems when the adhesive resin 122 is applied excessively in the adhesive resin 122 applying process or the glass element 107 is pressed on the adhesive 122 to mount the element, shifting the resin 122 along the substrate 100. That is, this causes such a phenomenon as a flow of the adhesive resin 122 into the V-groove 102 and the alignment mark 109.
The alignment mark 109 serves as a reference coordinate to calculate a mounting position of the element on the substrate 100 in an image recognition process when the element is mounted. When the adhesive resin 122 is flown into the alignment mark 109, the adhesive resin 122 thus casts a shadow to prevent the alignment mark 109 from being recognized accurately. Recognition error consequently occurs in image recognition, disabling to mount the element or leading to misalign the element.
As shown in FIG. 9, the adhesive resin 122 flown into the V-groove 102 fills an inside of the V-groove 102 to be fixed, thus covering a reflective layer 121. A route of the light for reception 120 delivered through an optical fiber is thus blocked by the adhesive resin 122 so that the light reception cannot normally reach a light receiving part of PD106, resulting in an error with the light for reception.
Patent Document 3 (Japanese Patent Publication 2000-183237) discloses a semiconductor apparatus, in which a semiconductor chip is mounted on a printed circuit board and illustrates a structure, in which an adhesive resin is prevented to spread from a surrounding of the semiconductor chip, thus enabling to mount in higher density.    Patent Document 1: Japanese Patent Publication H10-206678    Patent Document 2: Japanese Patent Publication 2006-154535    Patent Document 3: Japanese Patent Publication 2000-183237